The Ultraviolet Imaging Telescope, one of the three ultraviolet
telescopes of the Astro Observatory, flew on Space Shuttle
missions in December 1990 and March 1995. It was designed, built, and
operated by a team led by Theodore P. Stecher at Goddard Space Flight
Center.
UIT was proposed in 1978 as part of a program to fly small
("university-class") scientific experiments on the Spacelab modules
attached to the Space Shuttle. At that time, NASA anticipated that
there would be about 3 Shuttle/Spacelab missions each year dedicated
to astrophysics experiments (out of an envisioned 20 or so missions
annually). By late 1985, the Astro UV telescopes had been approved
for six missions. At the time of the Challenger accident in January
1986, Astro-1 was in the Shuttle Columbia payload bay ready for
the launch to follow the Challenger mission. In the aftermath of the
accident and in the face of the rapidly escalating costs of the
Shuttle itself, the Spacelab astrophysics program was drastically
reduced. Of the 200 experiments proposed in 1978, only the four
telescopes of the Astro-1 mission were actually flown.
UIT was a 38-cm Cassegrain telescope carrying two ultraviolet cameras
with 40 arc-minute diameter fields of view (150 times larger than the
field of the Hubble Space Telescope). The cameras operated in the
"far-UV" (120-200 nm) and "mid-UV" (200-320 nm) spectral ranges,
respectively, and carried a total of 12 filters. They employed image
intensifiers with very strong long-wavelength rejection to provide
pure UV images. Fine guidance was accomplished with an articulated
secondary mirror controlled by a signal from an externally mounted
15-cm star tracker containing a CCD detector. Final resolution for
point sources was typically 2.7 arc-seconds FWHM. During the two
Astro missions, UIT returned a total of 1570 data frames of 250
different astronomical targets.
The Astro UV payload consisted of UIT, the Hopkins Ultraviolet
Telescope (HUT), and the Wisconsin Ultraviolet Photo-Polarimeter
Experiment (WUPPE). HUT was a far-ultraviolet spectrometer (Johns
Hopkins University, led by A. F. Davidsen). WUPPE was a UV
spectro-polarimeter (University of Wisconsin, led by A. D. Code).
These three instruments were co-aligned and mounted on the Spacelab
Instrument Pointing System. They were operated simultaneously on a
given target by crew members from the Shuttle aft flight deck.
For Astro-1 (STS-35, 1990, Shuttle Columbia) the Broad-Band X-Ray
Telescope (BBXRT, P. Serlemitsos, Goddard Space Flight Center) was
operated independently on a separate pointing system. Astro-1
compiled a NASA record for delays: 33 different assigned launch dates
over 8 years, 12 complete target timelines planned (each 8 days long
at 1 second resolution), and 4 scrubs within 6 hours of launch. On
Astro-2 (STS-67, 1995, Shuttle Endeavour), the UV telescopes flew
alone. Astro-2 was the first NASA mission to have an active
Internet home page and logged over 2.5 million hits from over 200,000
people during its 15 day duration.